Oxidation of alkyl aromatics

ABSTRACT

Process of liquid phase oxidation of the alpha carbon atom of alkylbenzenes by a manganic or cobaltic salt and an acid activator with or without an oxidation-resistant solvent either in an inert atmosphere to produce lower oxidation products of the alpha carbon atom such as alcohols or their esters; or, in the presence of molecular oxygen, to produce higher oxidation products such as aromatic aldehydes, ketones or carboxyl acids.

United States Patent 1 1 de Raditzky DOstrowick et al.

[ OXIDATION OF ALKYL AROMATICS [7 5] Inventors: Pierre M. J. G. deRaditzky DOstrowick; Jacques D. V. Hanotier, both of Brussels. Belgium[73] Assignee: Labofina, Soc. An.,Brussels,

Belgium Notice: The portion of the term of this patent subsequent to May23, 1989. has been disclaimed.

[22] Filed: Nov. 17, I971 [21] Appl. No.: 199,722

Related US. Application Data [62] Division of Scr. No. 884,336. Dec. ll,1969. Pat. No.

[52] [1.8. CI. 260/488 CD; 260/515 R; 260/592; 260/599; 260/600 [5 l]Int. Cl. C07c 45/02 [58] Field of Search 260/524 M, 599. 592

[56] References Cited UNITED STATES PATENTS 780,404 l/l905 Bazlcn et al.260/524 *Apr. 8, 1975 3334.135 8/1967 lchikawa 260/524 3.665.030 5/1972dOstrowicketal 260/488 FOREIGN PATENTS OR APPLICATIONS 22.105 9/1900United Kingdom 260/524 Primary Examiner-Lorraine A. Weinberger AssistantExaminer-Richard D. Kelly [57] ABSTRACT Process of liquid phaseoxidation of the alpha carbon atom of alkylbenzenes by a manganic orcobaltic salt and an acid activator with or without anoxidationresistant solvent either in an inert atmosphere to producelower oxidation products of the alpha carbon atom such as alcohols ortheir esters; or. in the presence of molecular oxygen, to produce higheroxidation products such as aromatic aldehydes, ketones or carboxylacids.

9 Claims, No Drawings 1 OXIDATION OF ALKYL AROMATICS The presentinvention relates to a process for selective oxidation of alkylaromaticcompounds using an oxidizing system comprising a higher valentcobalt(lll) or manganese (Ill) salt of a carboxylic acid and thisapplication is a division of our copending application, Ser. No.884,336, filed Dec. ll, 1969, now US. Pat. No. 3,- 665,030, issued May23, l972, by streamline refile and a relatively strong acid.

Oxidation of alkylaromatic compounds into oxygenated products in theliquid phase with molecular oxygen in the presence of a heavy metalcatalyst is the best available to the chemical industry at this time.Its application remains restricted as a rule to the production ofcarboxylic acids. This-is principally due to the fact that to reach asufficient rate of reaction, stringent conditions such as hightemperatures and pressures must be applied so that intermediateoxidation products of the alcohol, aldehyde or ketonc type are rapidlyconverted into acids. During this process, the alkyl groups comprisingseveral atoms of carbon undergo a cleavage of the carbon-carbon bondsexcept for those joining these to the aromatic nucleus. For this reason,the method is applied principally for oxidation of methylaromatichydrocarbons like toluene and xylenes. Oxidations performed in the artunder milder conditions with various catalysts have been non-selectiveor inapplicable.

we have now discovered that by employing an oxidizing system comprisingthe cobalt or manganese salt of a carboxylic acid in higher valent formand a relatively strong acid, the oxidation of the alkylaromaticcompounds can be performed at distincly lower temperatures than thosepreviously required, with a higher rate of reaction and a greatlyimproved selectivity. We have found, that by appropriate selection ofthe components of the oxidizing system and of the operating conditions,the oxidation of the alkylaromatic compounds can be controlled to formside chain alcohols, mainly in the form of esters; or to form aromaticketones or aldehydes, depending on the structure of the alkylsubstituent; or to form aromatic carboxylic acids selectively asprincipal products. Analogously, starting with a polyalkylated aromaticcompound, the reaction can be limited to selectively oxidize a singlealkyl group or carried further to oxidize several alkyl side chains.Finally, the oxidizing system employed has an activity such that thealkylaromatic compounds further substituted by a deactivating group areattacked rapidly. Such deactivating groups are chloro, nitro, carboxylor other electron-attracting groups.

The main object of the present invention is to provide a process for theoxidation of alkylaromatic compounds, during which one or more alkylgroups thereof are converted quickly in satisfactory yield intooxygenated functions, with a high degree of selectivity and control. Itis a further object to provide a process of carrying out such oxidationsat low temperatures.

According to the present invention, alkylaromatic compounds having atleast one hydrogen atom at the alpha position to the aromatic nucleusare oxidized in 'the liquid phase at that alpha position at atemperature in the range of -30 C to +100 C, with an oxidizing systemcomprising the higher valent cobalt(lll) or higher valent manganese(lll) salt of a carboxylic acid and a stable acid whosedissociation'constant is higher than 10 or boron trifluoride, or amixture thereof.

The alkylaromatic compounds which are oxidized most satisfactorily bythe process of the invention are those which comprise at least one alkylradical having at least one hydrogen atom at the alpha position relativeto the aromatic ring. Although higher alkyl radicals can be oxidizedsuch as those having up to about 30 carbon atoms or even higher, thearomatic compounds with l to 6 alkyl radicals having from 1 to 4 carbonatoms are a preferred group of alkylaromatic compounds to be oxidizedsince they are easily and more economically available. Typicalalkylaromatics oxidized herein are the mono-, diand tri-alkylbenzenes,like toluene, ethylbenzene, cumene, 0-, m'-' or pxylenes, o-, m orp-diethylbenzenes and trimethyl benzenes. Polynuclear alkylaromaticcompounds such as the mono-, diand trialkylnaphthalenes, like methylnaphthalenes, ethyl naphthalenes and dimethylnaphthalenes are alsoeasily oxidized. Apart from these purely hydrocarbon compounds,alkylaromatic compounds substituted by other radicals, for example.chloro, bromo, iodo, fluoro, nitro or oxygenated radicals such as acyl,alkoxy, carboxyl, l-acyloxyalkyl, may also be oxidized. Typical suchsubstituted alkylaromatic compounds are p-chlorotoluene,p-bromoethylbenzene, m-nitrotoluene, o-acetyltoluene,4-methoxyethylbenzene, p-toluic acid, 4-methyl-l-naphthoic acid,p-methylbenzyl acetate, and the like.

In order that the oxidation of these compounds by the process of theinvention may be performed in the liquid phase, it is not essential, butoften useful. to employ a solvent. In particular cases, the oxidizingsystem is soluble in the liquid alkylaromatic compound to be oxidized,and the reaction can occur in the solution thus obtained. Mostfrequently, however, the reactants are desirably dissolved in a solventcommon to both. in general any liquid reasonably inert to oxidation, inwhich the alkylaromatic compound to be oxidized and the oxidizing systemare soluble, may be used. The fatty acids containing from 2 to 10 carbonatoms and their lower esters, preferably their methyl and t-butylesters, satisfactorily fulfill the preceding conditions. Acetic acid isa particularly advantageous solvent.

Among the metal compounds capable of oxidizing hydrocarbon or otherorganic substances, the cobalt- (lll) and manganeseflll) salts ofcarboxylic acids are preferred. They are powerful oxidizers; they aresatisfactorily soluble in such organic solvents; they are easilyproduced by known methods. From these points of view, the cobalt(lll)and manganese(lll) salts of fatty acids containing from 2 to 10 atoms ofcarbon, and preferably their acetates, are particularly satisfacory. Forexample, cobalt(lll) acetate may be produced by cooxidation ofcobalt(ll) acetate with acetaldehyde in acetic acid in the presence ofoxygen. Manganeseflll) acetate may be produced by oxidation ofmanganese(ll) acetate with potassium permanganate in acetic acid. Thecobalt(lll) and manganeseflll) salts of the other fatty acids can beproduced in analogous manner or by exchange reaction between these andcobalt(lll) acetate.

, A fundamental and important aspect of the present invention is thediscovery that the oxidizing power of these cobaltic and manganic saltsin respect of alkylaromatic compounds is enhanced considerably by thepresence'of a relatively strong inorganic or organic acid. The acidswhich display this activating effect are those whose dissociationconstant K is higher than 10'. They should be soluble in the reactionmedium and should not interfere with the reaction. Suitable acids aresulphuric acid (K l perochloric acid (K 1 p-toluenesulphonic acid (K ltrifluoroacetic acid (K 610"). trichloroacetic acid (K 210).dischloroacetic acid (K 3.3 X 10"). phosphoric acid (K 7.5 X 10 andmonochloroacetic acid (K 1.4 X l Some Lewis acids such as borontrifluoride. also have an activating action. The acids containingchlorine, bromine or iodine in ionic form. such as hydrochloric acid.hydrobromic acid or aluminium trichloride are unstable in the conditionsof the process and should be avoided.

The activating action ofthe acids defined above is exerted both on therate and the progress of the reaction. The effect is the more pronouncedthe stronger the acid and. up to a definite limit. the higher itsconcentration. On the other hand. the quantity of acid should becorrelated to the quantity of cobaltic or manganic salt employed. Forexample, if sulphuric acid is employed to activate a cobaltic salt. amolar ratio between acid and salt of approximately 2 is needed to reachmaximum activity. With an acid of lesser strength. such astrichloroacetic acid. a ratio from to is preferable. Although themechanism of the activation has not been clarified yet. the facts whichhave been set forth lead to the possibility that the cobaltic ormanganic salt reacts with the acid to produce a more oxidizing specieswhich is assumed to be principally responsible for the attack of thesubstrate. The following scheme can be envisaged accordingly. where theacid. the metal salt and the reactive species are representedrespectively by AH. M and M(lll):

It must be added. moreover. that the activating effect of a given acidcan vary with temperature. the nature of the metal salt and thereactivity of the substrate. For example. the activating action ofweaker acids such as trichloroacetic acid or manganic acetate is lesseffective. under identical conditions. than on cobaltic acetate; but. atincreased temperature. it is improved the more effectively with the morereactive substrate. These different factors should be taken into accountin selecting the oxidizing system and the conditions to apply to oxidizea particular substrate.

The activator allows the oxidation of alkylaromatics to be performed atlow temperature. more specifically within a temperature range of to 100C. In order that the reaction may be rapid as well as selective. it ispreferable to operate at temperatures between 0 and 60 C. The reactionwill frequently be too slow below 0 C. and the selectivity inadequateabove 60 C. y

The nature of the oxidation products obtained by the present process isdetermined by the structure of the alkyl substituent. the composition ofthe oxidizing system, and the operating conditions. To produce alcoholsin the form of esters. the reaction will be carried out in a carboxylicsolvent such as acetic acid and in the absence of oxygen. For example.in these conditions. eth ylbenzene can be converted almostquantitatively into the acetate of alpha-methylbenzyl alcohol by use ofan oxidizing system comprising a manganic or a cobaltic salt. The esterobtained may then be hydrolyzed to produce the corresponding alcohol. orpyrolyzed to produce styrene. Toluene is converted into benzyl acetateusing the same conditions. By.contrast, if it is preferred to obtainproducts containing a carbonyl function, it is advisable to operate inthe presence of oxygen and to make provision for vigorous stirring ofthe reaction mixture. in these conditions. ethylbenzene can be convertedinto acetophenone by preferential use of an oxidizing system comprisinga cobaltic salt. Analogously,

in the presence of oxygen, toluene can be oxidized into benzaldehyde orbenzoic acid, depending on whether a manganic or cobaltic salt isemployed. These particular examples clearly demonstrate theextraordinary selectivity of the process of the invention and the highdegree of control it provides by simple selection of the oxidizingsystem and of the operating conditions.

The effect of oxygen exemplified by the above instances is anotherimportant aspect of the present invention. The manner in which oxygenoperates in the reaction is not known with certainty. In the priorprocesses in which a compound ofa metal of high valency is employed asan oxidant. oxygen does not as a rule have an appreciable effect on thereaction. In the present case. it seems that the primary attack of thealkylaromatic compound leads to the formation of a free radical(reaction 3) which would then react with oxygen (reaction 4) to producea peroxy radical which is subsequently convertible to produce a ketone,an aldehyde or even an acid. as the case may be. In the absence ofoxygen. the radical would be oxidized in its turn. probably whileproducing a carbonium salt (reaction 5) which, in the presence of acarboxylic acid, would result in an ester (reaction 6) R 0 ROO ketone.aldehyde or acid R R'COOH ROCOR' H Corresponding to this pattern, theproportion of ester functions and of carbonyl functions in the reactionproducts is the result of competition between reactions (4) and (5 Itwill then be grasped that to promote the production of compounds havinga carbonyl function, it is necessary to choose conditions allowing thereaction (4) to predominate. that is to say to operate in the presenceof a gaseous phase containing oxygen and to make provision for vigorousstirring for rapid diffusion of the same into the liquid phase. Thisgaseous phase may consist of pure oxygen or of a mixture of oxygen withother gases which are inert in the conditions of the reaction, forexample air. The partial oxygen pressure rmay be between 0.1 andatmospheres. In particular cases. it is possible to apply pressureslying outside this range. For example, a lower pressure than 0.1atmosphere can be sufficient occasionally, subject to the condition ofproviding particularly effective stirring. On the other hand. higherpressures than 50 atmospheres may be applied, but those do not lead toan improvement in the results justifying additional plant investmentcosts. In the greater number of cases. an oxygen pressure of the orderof 0.2 to atmospheres will suffice to secure a high degree of conversioninto products having a carbonyl function.

The quantity of oxydant to be employed depends on the degree ofconversion required and on the nature of the products it is desired toobtain. The preceding pattern shows that at least two molar equivalentsof higher valent metal salts are needed to produce an ester in a highyield from a monoalkylbenzone. It might have been expected that agreater quantity of oxydant would be consumed to produce a ketone, analdehyde or an acid. In reality, the production of these compounds bythe process of the invention requires no more than a small quantity ofoxidant. For example, the production of acetophenone by oxidation ofethylbenzene by means of the system consisting of colbaltic acetate andtrichloroacetic acid in the presence of oxygen requires no more than 1.5to 2.2 atoms of cobalt(lll) per molecule of hydrocarbon. 1n the sameconditions. 0.3 to 0.5 atom of cobalt (lll) suffices to convert onemolecule of toluene into benzoic acid. These small values demonstratethat a definite degree of regeneration of the oxidizing system occurs inthe presence of oxygen. so that the quantity of oxidant consumed may inparticular cases be smaller than the quantity of product formed.

In the case of polyalkyl aromatic compounds, the oxidation may belimited to a single alkyl group. or extended to several. It is plain toone versed in the art that. to limit the oxidation, it is appropriate toshorten the period of reaction and to employ ana excess of polyalkylbenzene in comparison with the oxidizing system. whereas the inverse ofthese conditions will be preferable if it is desired to oxidize severalalkyl groups within one and the same molecule.

The invention will now be further described with reference to thefollowing examples:

EXAMPLE 1 This example illustrates the effect of sulphuric acid on theoxidizing power of manganic acetate with respect to alkylaromaticcompounds.

A solution containing 0.20 mol/Iiter of mdiethylbenzene and0.04mol/liter of manganic acetate in acetic acid was heated to 70 C forminutes. In a second assay, sulphuric acid was added to the solution atthe concentration of 0.5 mol/liter. after which this solution was keptat 25 C for ten minutes. A third assay was also carried out in thepresence of sulphuric acid but in the absence of substrate. At the endofthe three assays. the manganic ions present in the solution weredetermined by cerimetry. The results obtained are given in the followingtable.

'It is apparent that, in the presence of sulphuric acid, the

EXAMPLE II This example illustrates the effect of trichloroacetic acidon the oxidizing power of cobaltic acetate in respect of alkylaromaticcompounds. A solution containing 0.20 mol/liter of 2-ethylnaphthaleneand 0.05 mol/- liter of cobaltic acetate in acetic acid was ketp at 25 Cunder a nitrogen atmosphere at atmospheric pressure for 15 minutes. Thesame assay was repeated after addition of triehloroacetic acid to thesolution. in the proportion of 1.5 mol/liter. A third assay was alsocarried out in the presence of trichloroacetic acid. but in the absenceof substrate. At the end of the three assays the cobaltic ions presentin the solution were determined by cerimetry. The results obtained aregiven in the following table:

substrate triehloroaeetie acid reduced C o( 111) EXAMPLE 111 Thisexample illustrates the oxidation of toluene by means of the systemconsinsting of manganic acetate and sulphuric acid.

A solution containing 0.10 mol/liter of toluene. 0.21 mol/liter ofmanganic acetate and 1.0 mol/liter of sulphuric acid in acetic acid, waskept at 25 C. without stirring. under a nitrogen atmosphere atatmospheric pressure. 78 per cent of the manganic ions had been reducedafter one hour. An aliquot part of the reaction mixture was diluted withether and then treated at 0 C with anhydrous sodium carbonate until theacidity was neutralized. The ether solution was analyzed by vapour phasechromatography to establish the composition of the neutral oxidationproducts. The acid products were identified by analysis of anotheraliquot part of the reaction mixture. The combined results of bothanalyses show that 54 per cent of the toluene employed had beenconverted to yield the following oxidation products whose relativeproportions are expressed as molar percentages:

benzyl alcohol (mainly in the fomi of its 74 '7:

acetate ester) benzaldehyde 25 7t henzoic acid 1 '7:

EXAMPLE IV This example illustrates the effect of oxygen on theoxidation of toluene by means of the oxidizing system employed in thepreceding example.

.The experiment of Example III was repeated. but this time whilestirring the reaction mixture in the presence of pure oxygen atatmopsheric pressure. By treating and analyzing the reaction mixture asin Example lll. it was established that 65 percent of the tolueneemployed had been converted to yield the following oxidation productswhose relative proportions are expressed as molar percentages:

benzaldehyde 7l 7! benzyl alcohol 24 /1 (mainly in the form of itsacetate ester) benzoic acid 5 '/r Comparing the results of this exampleto those of Example lll. it is plain that in the presence of oxygen.toluene is converted preferentially into benzaldehyde rather than intobenzyl alcohol.

EXAMPLE V This example illustrates the oxidation of toluene by means ofthe system consisting of cobaltic acetate and trichloroacetic acid. inthe presence of oxygen.

A solution containing 0. l0 mol/liter of toluene, 0.20 mol/liter ofcobaltic acetate and 1.5 mol/liter of trichloroacetic acid in aceticacid was stireed at 25 C in the presence of pure oxygen at atmosphericpressure. 16 percent of the cobaltic ions had been reduced after fourhours. The reaction mixture was then treated and analyzed as in Examplelll. It was found that 81 percent of the toluene employed had beenconverted into pure benzoic acid.

In another experiment performed in identical manner but while extendingthe reaction period to 24 hours, the conversion of toluene into benzoicacid rose to 92 percent.

From this data it is calculated that the formation of a molecule ofbenzoic acid required the reduction of no more than 0.3 atom of cobalt.which demonstrates that a substantial proportion of the oxidant isregenerated "in situ during the reaction.

EXAMPLE Vl This example illustrates the use of propionic acid as asolvent.

The experiment of the preceding example was repeated, while replacingacetic acid with propionic acid. Analysis of the reaction mixture after24 hours showed that 55 percent of the toluene employed had beenconverted mainly to yield benzoic acid (98%) and small quantities ofbenzaldehyde (2%) Identical results were obtained by replacing cobalticacetate with cobaltic propionate.

EXAMPLE Vll This example illustrates the oxidation of ethylbenzene bymeans of the system consisting of manganic acetate and sulphuric acid.

A solution containing 0.10 mol/liter of ethylbenzene. 0.19 mol/liter ofmanganic acetate and 1.0 mol/liter of sulphuric acid in acetic acid waskept at 25 C. without stirring. under a nitrogen atmosphere atatmospheric pressure. 67 percent of the manganic ions had been reducedafter one hour. The reaction mixture was then treated and analyzed as inExample 1]]. It was thus established that 56 percent of the ethylbenzeneemployed had been converted to yield the following oxidation productswhose relative proportions are expressed as molar percentages.

alpha-methylbenzyl alcohol 9 (mainly in the form of its acetate ester)acetophenone benzoic acid EXAMPLE Vlll This example illustrates theoxidation of ethylbenzene by means of the system consisting of cobalticacetate and trifluoroacetic acid.

A solution containing 0.10 mol/liter of ethylbenzene, 0.20 mol/liter ofcobaltic acetate and 1.4 mol/liter of trifluoroacetic acid in aceticacid was kept at 25 C. without stirring, under a nitrogen atmosphere atatmospheric pressure. 77 percent of the cobaltic ions had been reducedafter 24 hours. The reaction mixture was then treated and analyzed as inExample lll. It was thus established that 56 percent of the ethylbenzeneemployed had been converted to yield the following oxidation productswhose relative proportions are expressed as molar percentages.

alpha-methylhenzyl alcohol 86 "/1 (mainly in the form of its acetateesters) acetophenone 9 "/2 benzoic acid 5 /2 By operating in identicalmanner but omitting the addition of trifluoroacetic acid to the system,only 9 percent of the ethylbenzene was converted to yield the followingproducts:

alpha-methylbenzyl alcohol 0 l: acetophcnone 67 7: benzoic acid 33 It isplain that in the absence of the acid activator, the reaction is notonly slowed down considerably, but its selectivity is completelychanged.

EXAMPLE lX This example illustrates the oxidation of ethylbenzene bymeans of the system consisting of cobaltic acetate and borontrifluoride.

The experiment of Example Vlll was repeated, but trifluoroacetic acidwas replaced by boron trifluoride in the same concentration. Analysis ofthe reaction mixture after three hours showed that 27 percent of theethylbenzene employed had been converted to yield the followingoxidation products whose relative proportions are expressed as molarpercentages:

alpha-methylhenzyl alcohol 87 2 (mainly in the form of its acetateester) acctophenonc 5 7r benzoic acid 8 7r By operating in identicalmanner, but without adding boron triluoride to the system. only percentof the hydr'ocarbon had been converted to yield the following products:

alpha-methylbenzyl alcohol acetophenone benzoic acid The action of theactivator set forth in the preceding example is confirmed in everyrespect by these results.

EXAMPLE X This example illustrates the oxidation of ethylbenzene bymeans of the system consisting of cobaltic acetate andp-toluenesulphonic acid.

The experiment of Example Vlll was repeated but trifluoroacetic acid wasreplaced with p-toluenesulphonic acid at the concentration of 0.3mol/liter. 33 percent of the cobaltic ions had been reduced after 24hours, and analysis showed that 14 percent of the ethylbenzene employedhad been converted to yield the following oxidation products whoserelative proportions are expressed as molar percentages:

alpha-methylbenzyl alcohol (mainly in the form of 75 7! its acetateester) acetophenone l5 "/1 benzoic acid EXA'MPLE Xl alpha-methylbenzylalcohol 88 7:

(mainly in the form of its acetate ester) acetophenone 9 7t benzoic acid3 "/1 EXAMPLE xu The experiment of Example Xl are repeated, butoperating at 60 C instead of C. 66 percent of the cobaltic ions had beenreduced after minutes. and analysis showed that of the ethylbenzeneemployed had been converted to yield the following oxidation productswhose relative proportions are expressed as molar percentages:

alpha-methylhenzyl alcohol 86 (mainly in the form of its acetate ester)acetophenone 7 benzoic acid 7 Compared to those of Example XI, theseresults show that an increase in the temperature can speed up thereaction without appreciably changing its selectivity.

EXAMPLE Xlll This example illustrates the effect of oxygen on theoxidation of ethylbenzene by means of the oxidizing system employed inExamples Xl and XI].

A solution containing 0.10 mol/liter of ethylbenzene, 0.20 mol/liter ofcobaltic acetate and 1.5 mol/liter of trichloroacetic acid in aceticacid was stirred at 25 C in the presence of pure oxygen at atmosphericpressure. 62 of the cobaltic ions had been reduced after 4 hours. Thereaction mixture was then treated and analyzed as in Example ll]. It wasthus established that 67 percent of the ethylbenzene had been convertedto yield the following oxidation products whose relative proportions areexpressed as molar percentages:

acetophenone 71 alpha-methylbenzyl alcohol l5 l1 (partially in the formof its acetate cster) benzoic acid 6 9 By comparing these results tothose of Examples XI and Xll, it is plain that in the presence ofoxygen. ethylbenzene is converted mainly into ketone rather than intoalcohol.

EXAMPLE XlV The experiment of Example Xlll was repeated. but on thisoccasion operating under an oxygen pressure of 10 kg/cm2. Analysis ofthe reaction mixture after 4 hours showed that 48 percent of theethylbenzene employed had been converted to yield the followingoxidation products whose relative proportions are expressed as molasrpercentages:

acetophenone X4 9;

alpha-methylbenzyl alcohol 16 92 (partially in the form of its acetateester) benzoic acid undetectable By comparing these results to those ofExample Xlll, it is apparent that the proportion of acetophenone hasbeen increased slightly by operating under a higher oxygen pressure. Noadditional increase is observed, however, if the test is performedunder, the oxygen pressure of 30 kg/cm2.

EXAMPLE XV This example illustrates the use of methyl acetate as asolvent.

A solution containing 0.10 mol/liter of ethylbenzene. 0.2l mol/liter ofcobaltic acetate and 1.5 mol/liter of trichloroacetic acid in methylacetate was kept at 25 C. without stirring, under-a nitrogen atmosphereat atmospheric pressure. 44 percent of the cobaltic ions had beenreduced after 5 hours. The reaction mixture was then treated andanalyzed as in Example lll. It was thus established that 14 percent ofthe ethylbenzene employed had been converted to yield the followingoxidation products whose relative proportions are expressed as molarpercentages:

alpha-methylbenzyl alcohol 73 71 (mainly in the form of its acetateester) acetophenone 22 '7:

benzoic acid 5 '4 By operating in analogous manner but in the presenceof pure oxygen instead of an atmosphere of nitrogen, acetophenonebecomes the principal product.

EXAMPLEXVl This example illustrates the use of t-butyl acetate as asolvent.

The experiment of Example XV was repeated while replacing methyl acetatewith t-butyl acetate. 45 percent of the cobaltic ions had been reducedafter three hours. and analysis showed that 1 1 percent of theethylbenzene employed had been converted to yield the followingoxidation products whose relative proportions are expressed as molarpercentages:

alpha-methylbenzyl alcohol 82 7:

(mainly in the form of its acetate ester) acetophenone 18 71 EXAMPLEXVll This example illustrates the use of pelargonic acid as a solvent.

A solution containing 0.51 mol/liter of ethylbenzene. 0.17 mol/liter ofcobaltic acetate and 1.5 mol/liter of trichloroacetic acid in pelargonicacid was kept at 25 C. without stirring, under a nitrogen atmosphere atatmospheric pressure. 78 percent of the cobaltic ions had been reducedafter 24 hours. The reaction mixture was then neutralized by means ofalcoholic potash and subjected to specification for 4 hours in suchmanner as to hydrolyze the pelargonic esters formed during the reaction,to facilitate the identification of the oxidation products ofethylbenzene. After filtering the insoluble salts. the alcoholicsolution thus obtained was analyzed directly by vapor phasechromatography. The analysis enabled to identify the following oxidationproducts whose relative proportions are expressed as molar percentages:

alpha-meth \'lbenzyl alcohol acetophenone EXAMPLE XVlll This exampleillustrates the possibility of not employing any solvent.

A solution containing 0.2 mol/liter of cobaltic acetate and 1.5mol/liter of trichloroacetic acid in ethylbenzene was kept at 25 C.without stirring, under a nitrogen atmosphere at atmospheric pressure.59 percent of the cobaltic ions had been reduced after thirty minutes.Analysis of the reaction mixture by a method analogous to that describedin Example 111 enabled to identify the following oxidation productswhose relative proportions are expressed as molar percentages:

aeetophenone 67 /& alpha-methylbenzyl alcohol 31 alpha-methylbenzylacetate 2 "/1 benzoic acid 0 /1 This example also shows that, in theabsence ofa carboxylic solvent, the formation of ester is negligible, asin the presence of oxygen.

EXAMPLE XIX This example illustrates the oxidation of cumene by means ofthe system consisting of cobaltic acetate and trichloroacetic acid inthe presence of oxygen.

A solution containing 0.10 mol/liter of cumene, 0.20 mol/liter ofcobaltic acetate and 1.5 mol/liter of trichloroacetic acid in aceticacid, was stirred at 25 C in the presence of pure oxygen at atmosphericpressure. 54 percent of the cobaltic ions had been reduced after 24hours. The reaction mixture was then treated and analyzed as in Examplelll. It was thus established that 2] percent of the cumene employed hadbeen converted to yield the following oxidation products whose relativeproportions are expressed as molar percentages:

s. Ll okll sea EXAMPLE XX This example illustrates the oxidation of 2-ethylnaphthalene by means of the system consisting of cobaltic acetateand trichloroacetic acid.

A solution containing 0.10 mol/liter of 2- ethylnaphthalene, 0.19mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acidin acetic acid was kept at 25 C, without stirring, under a nitrogenatmosphere at atmospheric pressure. 71 percent of the cobaltic ions hadbeen reduced after 30 minutes. The analysis of the ether extractobtained as described in Example 111 showed that 57 percent of the 2-ethylnaphthalene employed had been converted to yield the followingoxidation products whose relative proportions are expressed as molarpercentages:

2( l-hydroxycthyl )naphthalenc 98 Z (mainly in the fonn of its acetateester) Z-acetylnaphthalene 2 71 EXAMPLE XXl The experiment of thepreceding example was repeated at 0 C instead of at 25 C. whileemploying propionic acid instead of acetic acid as a solvent. 43 percentof the cobaltic ions had been reduced after 5 hours. and analysis showedthat 21 percent of the 2- ethylnaphthalene employed had been convertedto yield the following oxidation products whose relative proportions areexpressed as molar percentages:

2-( l-hydroxyethyl)naphthalene (mainly in the 82 71 form of itspropionate ester) 2-acetylnaphthalene l8 7:

EXAMPLE XXll This example illustrates the possibility of operating atlower temperatures than 0 C.

A solution containing 0.51 mol/liter of 2- ethylnaphthalene, 0.18mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acidin propionic acid was kept at -20 C without stirring. under anatmosphere of nitrogen at atmospheric pressure. 47 percent of thecobaltic ions had been reduced after 5 hours, and analysis showed that 5percent of the 2- 2-( l-hydroxyethyl )naphthalene 94 (mainly in the formof its propionic ester) Z-acetylnaphthalene 6 "/1 EXAMPLE XXlll Thisexample illustrates the oxidation of pchlorotoluene by means of thesystem consisting of manganic acetate and sulphuric acid.

A solution containing 0.10 mol/liter of pchlorotoluene, 0.2l mol/literof manganic acetate and 1.0 mol/liter of sulphuric acid in acetic acidwas kept at 25 C, without stirring, under a nitrogen atmosphere atatmospheric pressure. 87 percent of the manganic ions had been reducedafter 2 hours. The analysis of the ether extract obtained as describedin Example Ill showed that 62 percent of the p-chlorotoluene employedhad been converted to yield the following oxidation products whoserelative proportions are expressed as molar percentages:

p-chlorobenzyl alcohol 74 "/2 (mainly in the form of its acetate ester)p-chlorobenzaldehyde 26 EXAMPLE XXIV This example illustrates theoxidation of pmethoxytoluene by means of the system consisting ofcobaltic acetate and trichloroacetic acid.

A solution containing 0.10 mol/liter of pmethoxytoluene. 0.21 mol/literof cobaltic acetate and L5 mol/liter of trichloroacetic acid was kept atC. without stirring. under a nitrogen atmosphere at atmosphericpressure. 88 percent of the cobaltic ions had been reduced after 5minutes. The analysis of the ether extract obtained as described inExample lll showed that 56 percent of the p-methoxytoluene employed hadbeen converted to yield the following oxidation products whose relativeproportions are expressed as molar percentages:

p-methoxybenzyl alcohol 82 7( (mainly in the form of its acetate ester)p-methoxybenzaldehyde l8 "/1 EXAMPLE XXV This example illustrates theoxidation of mnitrotolucne by means of the system consisting of cobalticacetate and trichloroacetic acid.

A solution containing 0.50 mol/liter of mnitrotoluene, 0.19 mol/liter ofcobaltic acetate and 1.5 mol/liter of trichloroacetic acid in aceticacid was kept at 25 C, without stirring, under a nitrogen atmosphere atatmospheric pressure. 51 percent of the cobaltic ions had been reducedafter 3 hours. The analysis of the ether extract obtained as describedin Example lll enabled to identify the following oxidation productswhose relative proportions are expressed as molar percentages:

m-nitrobenzyl alcohol 7r (mainly in the form of its acetate ester)n-nitrobenzaldehyde l0 '7:

EXAMPLE XXVI This example illustrates the oxidation of p-xylene by meansof the system consisting of cobaltic acetate and trichloroacetic acid,in the presence of oxygen.

A solution containing 0.05 moi/liter of p-xylene, 0.20 mol/liter ofcobaltic acetate and 1.5 mol/liter of trichloroacetic acid was stirredat 25 C in the presence of pure oxygen at atmospheric pressure. 19percent of the cobaltic ions had been reduced after 24 hours. Thereaction mixture was then diluted with an equal volume of ether. Aninsoluble residue was filtered, washed for a first time with a mixtureof acetic acid and ether l/l a second time with water, then dried. Theinfrared spectrum of the product thus isolated was identical to that ofpure terephtalic acid and its acidity amounted to 11.98 meq./g(theoretical value: 12.04). On the other hand, the ether filtrates werecollected before being treated and analyzed as described in Example lll.It was thus established that 59 percent of the p-xylene employed hadbeen converted to yield the following oxidation products whose relativeproportions are expressed as molar percentages:

terephtalic acid p-toluic acid EXAMPLE XXVll This example illustratesthe oxidation of mdiethylbenzene by means of the system consisting ofmanganic acetate and sulphuric acid.

A solution containing 0.05 mol/liter of mdiethylbenzene. 0.22 mol/literof manganic acetate and 1.0 mol/liter of sulphuric acid in acetic acidwas kept at 25 C under a nitrogen atmosphere at atmospheric pressure. 63percent of the manganic ions had been reduced after 30 minutes. Thereaction mixture was then diluted with a saturated solution of sodiumchloride in water, then subjected to repeated extractions with ether.The ether extract was neutralized by an aqueous solution of sodiumcarbonate and dried over anhydrous sodium sulphate before being analyzedby vapor phase chromatography. Analysis showed that the total quantityof the m-diethylbenzene employed had been converted, yielding thefollowing oxidation products the relative proportions of which areexpressed as molar percentages:

m'( l-hydroxyethyl)ethylbenzenc 78 '7( (mainly in the form of itsacetate ester) m-bis( l-hydroxyethyl)benzene l8 "/1 (in the form of itsdiacetate ester) m-ethylacetophcnone 4 "/2 By operating under the sameconditions but omitting sulphuric acid, only 0.2 percent of the manganicions were reduced after one hour (that being twice the time necessaryhereinabove) and no oxidation products were detectable by analysis.

EXAMPLE XXVIII The experiment of Example XXVI] was repeated, ex-

cept that the concentration of manganic acetate as increased byapproximately 30 per cent (0.28 mol/liter instead of 0.22) and thereaction was extended to a total period of hours. With these conditions.97 percent of the manganic ions were reduced and the oxidation productswere shown to be distributed, in mols. in the following manner:

m-bis( l-hydroxyethyl)bcnzecne 6t 7? (in the form of its diacetateester) m-( l-hydroxyethyl)ethylbenzene lo "/1 (mainly in the form of itsacetate ester) m-ethylacetophcnone Zl 7r m-diacetylbenzene 2 "/2Compared to those of Example XX'VIl. these results show that. byincreasing the quantity of oxidant in comparison to the substrate, andby extending the reaction time, it is possible to oxidize the two alkylsubstituents of a dialkylaromatic compound.

EXAMPLE XXIX The experiment of Example XXVII was repeated except thatthe concentration of m-diethylbenzene was doubled (0.10 mol/literinstead of 0.05). The reaction was extremely fast. since 77 percent ofthe manganic ions were reduced within 3 minutes.

The reaction mixture was then treated by an extraction method analogousto that applied in Examle XXVll. and also analyzed by vapor phasechromatography. Analysis showed that 85 percent of the mdiethylbenzeneemployed had been converted to yield the following oxidation productswhose relative proportions are the following oxidation products whoserelative proportions are expressed as molar percentages:

m-( l-hydroxyethyl)ethylhenzene 96 "/2 (mainly in the form of itsacetate ester) m-bist l-hydroxy'ethyl )benzenc 3 /2 (mainly in the formof its diacetate ester) m-cthylacetophenone l Compared to those ofExample XXVll. these results show the gain in reaction rate and inselectivity achieved when increasing the amount of substrate compared tothe oxidant.

EXAMPLE XXX m-( l-hydroxyethyl)ethylbenzene 97 7:

(mainly in the form of its acetate ester) m-bis( l-hydroxyethyl )benzenetraces (in the form of its diacctate ester) 1 7 methylaeetophenoneEXAMPLE XXXI This example illustrates the oxidation of mdiethylbenzeneby means of the system consisting of 5 cobaltic acetate and sulphuricacid.

A solution containing 0.05 mol/liter of mdiethylbenzene, 0.20 mol/literof cobaltic acetate and 0.5 moi/liter of sulphuric acid in acetic acidwas kept at C under a nitrogen atmosphere at atmospheric pressure. 44percent of the cobaltic ions had been reduced after 20 minutes. Thereaction mixture was then treated and analyzed as in Example XXVI]. Itwas thus established that 55 percent of the m-diethylbenzene employedhad been converted to yield the following oxidation products whoserelative proportions are expressed as molar percentages:

m-t l-hydroxyethyl)ethylbenzene 70 70 (mainly in the form of its acetateester) m-bis( l-hydroxyethyl)benzene 4 9? (in the form of its diacetateester) m-ethylaeetophenone 24 '7: m-( l-hydroxyethyl)acetophenone 2 '7:

EXAMPLE XXXll m-( l-hydroxyethyl)ethylbenzene 79 /r 40 (mainly in theform of its acetate ester) m-bis( l-hydroxyethyl )benzene 6 "/1 (in theform of its diacetate ester) m-ethylacetophenone l5 '7:

EXAMPLE XXXIII This example illustrates the oxidation of mdiethylbenzeneby means of the system consisting of cobaltic acetate and perchloricacid.

The experiment of Example XXXI was repeated while substitutingperchloric acid at the concentration of 1.0 mol/liter for sulphuricacid. 47 percent of the cobaltic ions had been reduced after tenminutes. and analysis showed that 79 percent of the mdiethylbenzeneemployed had been converted to yield the following oxidation productswhose relative proportions are expressed as molar percentages: n

m-( l-hydroxyethyl)ethylbenzene 86 '71 (mainly in the form of itsacetate ester) m-his( l-hydroxyethyl)benzene 4 it (in the form of itsdiacctate ester) m-ethylacetophenone l0 7:

EXAMPLE XXXIV This example illustrates the oxidation of mdiethylbenzeneby the system consisting of cobaltic acetate and trichloroacetic acid.

The experiment of Example XXXl was repeated while substitutingtrichloroacetic acid at the concentration of 1.5 moi/liter for sulphuricacid. 23 percent of the cobaltic ions had been reduced after 30 minutes.and analysis showed that 42 percent of the mdiethylbenzene employed hadbeen converted to yield the following oxidation products whose relativeproportions are expressed as molar percentages:

m-( l-hydroxyethyl )ethylbenzene 90 "/1 (mainly in the form of itsacetate ester) m-bis( l-hydroxyethyhbenzene 3 7! (in the form of itsdiacetate ester) m-ethylacetophenone 7 '71 By operating in the sameconditions but in the absence of trichloroacetic acid, only 10 percentof the cobaltic ions were reduced after 2 hours (this being a periodwhich is 4 times as long as in the experiment hereinabove) and only 9percent of the m-diethylbenzene was converted to yield the followingproducts:

m-( l-hydroxyethyl)ethylbenzene 36 "/1 (in the form of its acetateester) m-ethylacetophenone 64 "/1 Hereagain. it is apparent that in theabsence of the acid activator, the reaction is not only slowed downconsiderably. but its selectivlity is changed completely.

EXAM'PLE xxxv m-ethylacetophenone 66 "/1 m-( l-hydroxyethyl)ethylhenzenel7 acetate ester of m l-hydroxyethyl)ethylbcnzene l6 "/1 m-bis(l-hydroxyethyl)benzene l By continuing the same experiment up to 24hours, 57 percent of the cobaltic ions were reduced and 89 percent ofthe m-diethylbenzene employed was converted to yield the followingproducts:

m-ethylacetophenone 7 m-( l-hydroxyethyl )ethylbenzenc acetate ester ofm-( 1-hydroxyethyl)ethylbenzene m-bis( l-h \droxyethyl )benzene m-(l-hydroxyethyl )acetophenone m-diacetylhenzene By comparing theseresults to those of Example XXXlV. it is apparent that in the presenceof oxygen the hydrocarbon is oxidized preferentially into ketone ratherthan into alcohol.

EXAMPLE xxxvr This example illustrates the oxidation of the acetate ofm-( l-hydroxyethyl )ethylbenzene by means of the system consisting ofcobaltic acetate and phosphoric acid.

A solution containing 0.05 mol/liter of the acetate of m-(l-hydroxyethyl)ethylbenzene. 0.10 moi/liter of cobaltic acetate and 1.0mol/liter of phosphoric acid was kept at 25C undera nitrogen atmosphereat atmospheric pressure. 43 percent of the cobaltic ions had beenreduced after 4 hours. The reaction mixture was then treated by anextraction method analogous to that employed in Example XXVI] and theextract was also analyzed by.vapor phase chromatography. It was thusestablished that 25 percent of the ester employed had been converted toyield the following oxidation products whose relative proportions areexpressed as molar percentages:

m-bis( l-hydroxyethyl )benzene (mainly in the form of its diacetateester) m-ethylacetophenone 3 m-( l-hydroxyethyl)acctophenone 2 EXAMPLEXXXVI] This example illustrates the oxidation of durene by means of thesystem consisting of cobaltic acetate and trichloroacetic acid.

A solution containing 0.05 mol/liter of durene. 0.30 mol/liter ofcobaltic acetate and 1.5 mol/liter of trichloroacetic acid in aceticacid was stirred at 60 C in the presence of pure oxygen under a pressureof 10 kg/cm2. 78 percent of the cobaltic ions had been reduced after 24hours. After evaporation of the solvent. the acidic products wereseparated by extraction with aqueous potash followed by acidificationwith hydrogen chloride; they were then analyzed by paper chromatography.It was thus established that durene had been quantitatively converted toyield the following oxidation products whose relative proportions areexpressed as molar percentages:

durylic acid 4 7t dimethylphthalic acids 68 71 methyltrimellitic acid 237: pyromellitic acid 5 7:

What is claimed is:

l. The process of oxidizing an alkyl carbocyclic aromatic compoundhaving at least one methyl radical directly linked to the aromaticnucleus, to selectively produce an aromatic aldehyde, comprisingreacting said alkylaromatic compound in the liquid phase with a saltconsisting essentially of a manganic carboxylate in the presence of anactivator selected from the group consisting of the acids having adissociation constant higher than 10" and which are stable in theconditions of the reaction, boron trifluoride, and mixtures thereof, ata temperature between 30 and C, and under a partial pressure of oxygenbetween 0.1 and 50 atmospheres.

2. The process as defined in claim 1 wherein the aromatic nucleus ofsaid alkylaroinatic compound is selected from the group consisting ofbenzene and naphthalene.

3. The process as defined in claim 2 wherein said aromatic nucleus hasfrom I to 6 alkyl substituents each having from I to 4 carbon atoms.

4. The process as defined in claim 2 wherein said aromatic nucleus isfurther substituted with a polar radical selected from the groupconsisting of halo. nitro. acyl. l-acyloxyalkyl. carboxy and alkoxy.

5. The process as defined in claim 1 wherein said manganic carboxylateis the salt of a fatty acid having from 2 to 19 carbon atoms.

6. The process as defined in claim 5 wherein the manganic salt ismanganic acetate. 4

7. The process as defined in claim 1 wherein said activator is selectedfrom the group consisting of sulfuric, perchloric, p-toluenesulphonic,trifluoroacetic, trichloroacetic, tribromoacetic, dichloroacetic,phosphoric and monochloroacetic acids, boron trifluoride and mixturesthereof.

8. The process as defined in claim 1 wherein the reaction is effected inthe presence of a solvent selected from the group consisting of thefatty acids having from 2 to 10 carbon atoms. and the methyl and t-butylesters of said fatty acids.

9. The process as defined in claim 8 wherein said solvent is aceticacid.

1. THE PROCESS OF OXIDIZING AN ALKYL CARBOCYCLIC AROMATIC COMPOUND HAVING AT LEAST ONE METHYL RADICAL DIRECTLY LINKED TO THE AROMATIC NUCLEUS, TO SELECTIVELY PRODUCE AN AROMATIC ALDEHYDE, COMPRISING REACTING SAID ALKYLAROMATIC COMPOUND IN THE LIQUID PHASE WITH A SALT CONSISTING ESSENTIALLY OF A MANGANIC CARBOXYLATE IN THE PRESENCE OF AN ACTIVATOR SELECTED FROM THE GROUP CONSISTING OF THE ACIDS HAVING A DISSOCIATION CONSTANT HIGHER THAN 10-3 AND WHICH ARE STABLE IN THE CONDITIONS OF THE REACTION, BORON TRIFLUORIDE, AND MIXTURES THEREOF, AT A TEMPERATURE BETWEEN -30* AND 100*C, AND UNDER A PARTIAL PRESSURE OF OXYGEN BETWEEN 0.1 AND 50 ATMOSPHERES.
 2. The process as defined in claim 1 wherein the aromatic nucleus of said alkylaromatic compound is selected from the group consisting of benzene
 3. The process as defined in claim 2 wherein said aromatic nucleus has from
 4. The process as defined in claim 2 wherein said aromatic nucleus is further substituted with a polar radical selected from the group
 5. The process as defined in claim 1 wherein said manganic carboxylate is
 6. The process as defined in claim 5 wherein the manganic salt is manganic
 7. The process as defined in claim 1 wherein said activator is selected from the group consisting of sulfuric, perchloric, p-toluenesulphonic, trifluoroacetic, trichloroacetic, tribromoacetic, dichloroacetic, phosphoric and monochloroacetic acids, boron trifluoride and mixtures
 8. The process as defined in claim 1 wherein the reaction is effected in the presence of a solvent selected from the group consisting of the fatty acids having from 2 to 10 carbon atoms, and the methyl and t-butyl esters
 9. The process as defined in claim 8 wherein said solvent is acetic acid. 